Infinitely variable friction gear

ABSTRACT

The infinitely variable friction wheel transmission with two transmission units and a traction element wound around the carriers of each respective transmission unit in the form of a Figure-8, comprises for each carrier a compensating element which exerts a restoring force on the carriers when a differential angle occurs between the two carriers.

FIELD OF THE INVENTION

The present invention concerns an infinitely variable friction wheeltransmission.

BACKGROUND OF THE INVENTION

An infinitely variable friction wheel transmission of this type usuallyhas input and output discs arranged coaxially on a common shaft,arranged together in pairs and whose inside surfaces are designed intoroidal shape, with friction wheels arranged between the pairs of inputand output discs. These friction wheels are in frictional contact withboth the input discs and the output discs, and transfer the torque to betransmitted from the input disc to the output disc by virtue offriction-force contact, whre the rotation speed of the friction wheelsbeing the higher the larger is the distance between their point ofcontact with the input disc and the rotation axis. In contrast, therotation speed of the output discs is higher the closer the point ofcontact between the friction wheel and the output disc is to therotation axis. Accordingly, by swivelling the friction wheels, therotation speed of the output discs can be infinitely variably adjustedas desired. For this purpose, the rotation axles of the friction wheelsare in each case mounted on a carrier which can be controlled by meansof a swivelling device.

Such an infinitely variable friction wheel transmission is described indetail in DE 197 54 725 by the present applicant. This transmissioncomprises two transmission units arranged coaxially with the inputshaft, each transmission unit having an input disc and an output discbetween which, in each case, are arranged two friction wheels, eachfriction wheel being attached on a carrier that can be swivelled. Boththe input and the output discs are mounted on a torque shaft which canbe displaced slightly in the axial direction relative to the inputshaft. The input disc of one transmission unit is rotationally fixedwith respect to the torque shaft, but is mounted on the latter so thatit can slide axially on it. The input disc of the other transmissionunit too is connected to the torque shaft in a rotationally fixed way byvirtue of drive gearing. The two output discs of the two transmissionunits are arranged mirror-symmetrically and adjacent to one another inthe transmission, and are arranged on a common bushing, so that a torquetransmitted from one input disc to its associated output disc and atorque transmitted from the other input disc to its associated outputdisc, are transmitted from the two output discs in rotationally fixedconnection with the bushing to a gear-wheel that meshes with a gearwheelof an output shaft. A roller-shaped pressing mechanism acts upon one ofthe input discs, which is mounted so as to be displaceable in the axialdirection on the input shaft but is in a rotationally fixed connectionwith it.

In the known infinitely variable friction wheel transmissions, thetransmission ratio is usually adjusted by moving the friction wheelstangentially with respect to the transmission axle, such that, however,swivel forces from the input and output discs act on the friction wheelarranged between them, since to transfer the torque these discs have tobe pressed against the friction wheel. In conventional infinitelyvariable friction wheel transmissions the friction wheel in eachtransmission unit is arranged such that its swivel axis is positioned atthe mid-point of the torus formed by the associated input and outputdiscs. Thus, at the contact point of the friction wheel with itsassociated input and output discs, so-termed normal forces are producedwhen the transmission ratio is adjusted.

To avoid the possibility that the normal forces occurring duringtransmission ratio adjustment are unequal, the torque moment on thefriction wheel resulting from this might produce an undesired change ofthe transmission ratio of the transmission, it has already been proposedin DE 198 26 057 by the present applicant to compensate for a possibledifference in the normal forces by producing a control force, such thatwith the friction wheel held axially, this control force which leads totilting of the friction wheel, can be applied to one of the twoassociated discs, while when one of the discs is axially fixed, thecontrol force acts on the friction wheel.

It has also already been proposed to support the friction wheels in aninfinitely variable friction wheel transmission by means of twoconnecting rods which oppose the occurring reaction forces. In this, theswivelling movement of the friction wheels is made possible by rollerbearings; this design, however, has the disadvantage that the weight ofthe friction wheel transmission is higher and there is no coupling ofthe swivelling movements of two carriers arranged in a transmission unitfor the friction wheels.

Further, an infinitely variable friction wheel transmission has beenproposed, in which at the top and bottom ends of the carriers in any onetransmission unit a traction element is provided, for example an endlesscable, which passes around the corresponding ends of the carriersessentially in a circle and which, to produce synchronous swivellingmovements of the carriers in opposite directions, is arranged in theform of a Figure-8, with a crossover point mid-way between the twocarriers. This arrangement both takes up the reaction forces on thefriction wheels and also synchronizes the swivel angle of the twoassociated carriers in each transmission unit.

Now, if the traction element is used in such manner that no differentialangle is possible between the carriers, i.e., the play between thetraction element and the carrier is very small, manufacturing tolerancescan lead to forced slippage under the friction wheels. If the tractionelement is used such that there is large play between the tractionelement and the carrier, then the necessary coupling between thecarriers will only exist when there is already a large differentialangle between the two carriers.

The purpose of the present invention is to provide a coupling betweenthe two carriers of any one transmission unit, which enables a certain,specified differential angle between the two carriers to be set but, atthe same time, when a differential angle occurs, a restoring force onthe corresponding carrier is produced.

SUMMARY OF THE INVENTION

According to the invention, then, it is provided that a compensatingelement is associated with each carrier in a transmission unit, whichbrings about effective coupling of the two carriers of the transmissionunit such that when a differential angle occurs between the twocarriers, a restoring force is exerted on the carrier. The compensatingelements are advantageously inserted as connection elements in thetraction element.

In an example of a preferred embodiment, the compensating elementcomprises a support disc in contact with a spring surrounded by asleeve, which is fitted so that it can move within a bushing against theforce of another spring, while the other section of the traction elementis attached to the center of the support disc.

The provision of a compensating element for each traction elementprovides the advantage that when a differential angle occurs, arestoring force is exerted on both carriers, whose effect is to reducethe differential angle. At the same time, tolerances in the mounting forthe traction element and in the traction element itself can becompensated by the gradual rise of the restoring force, without leadingto forced slippage at the contact points.

The manufacturing tolerances of the components, i.e., the holder for thetraction element and the traction element itself, can be correspondinglygreater. The behavior of the infinitely variable friction wheeltransmission can be affected by choosing different characteristics forthe springs used.

At the same time, the stability of the friction wheel transmission isincreased by this type of coupling; dampers provided in the compensatingelement can damp any additional oscillations that occur.

BRIEF DESCRIPTION OF THE DRAWINGS

Below, the invention is explained in more detail with reference to thedrawing in which two advantageous example embodiments are illustrated.The figures show:

FIG. 1 is a radial cross-section through a transmission unit of aninfinitely variable friction wheel transmission;

FIG. 2 is a schematic plan view of a traction element with insertedcompensating element;

FIG. 3 is an enlarged representation of a compensating element; and

FIG. 4 is a partial representation of a traction element with anotherexample embodiment of a compensating element

DETAILED DESCRIPTION OF THE INVENTION

Infinitely variable friction wheel variators are well known to thosefamiliar with the subject, so that in what follows, only thosecomponents necessary for understanding the invention are described andillustrated. The same components are denoted by the same referencenumbers in the various figures.

The two swivelling carriers for the friction wheels in a transmissionunit are referenced as 1 and 2. A traction element indexed 3 which, asviewed in FIG. 1, is provided at the bottom ends of the two carriers 1,2 for the friction wheels, wraps around the carriers 1, 2 essentially ina circle, so that the two carriers 1, 2 are coupled in relation to theirswivel angle. For this, the traction element 3 is guided by holders 5 onthe carriers 1, 2.

According to the invention, a so-termed phi-coupling is now providedbetween the two carriers 1, 2, in that two compensating elements 4 areinserted in the traction element 3, such that a specified differentialangle between the two carriers 1, 2 can occur but, at the same time, arestoring force is exerted on the carriers.

FIG. 3 shows a section through one of the compensating elements. When adifferential angle (phi1−phi2) occurs, a support disc 9 is pressedagainst a spring 6 so as to produce a restoring force in the tractionelement 3 on one of the two carriers 1, 2. By means of a series orparallel arrangement of various spring elements 6, 7 the restoring forcecan be adjusted as a function of the differential angle and otherparameters.

The maximum permissible differential angle can be limited by a sleeve.Advantageously, the restoring force on the carriers is small for a smalldifferential angle, so that manufacturing tolerances will not result inlarge restoring forces. In contrast, with larger differential angles itis advantageous for the restoring force to increase steeply so that ifoscillations occur the effect of this phi-coupling is brought into play.Equally well, a damper can be integrated in the compensating element 4.

One end of the traction element 3 is connected to the support disc 9 bymeans of a locking disc 10, while the other end of the traction element3 is connected to the bushing 11 by means of a locking disc 10.

In the example embodiment of a compensating element shown in FIG. 4, theholder for the traction element 3 is again referenced as 5; the carrier1 has a projection 14 which engages in a corresponding recess such thatits rotation is limited by two abutments 12, 13. Two springs 15, 16 arein each case attached at one end to the holder 5 for the tractionelement 3 and are connected at the other end to the projection 14 of thecarrier 1. Here too, the size of the restoring force on the carriers canbe influenced by an appropriate choice of the characteristics of thesprings.

Reference numbers 1 Carrier 2 Carrier 3 Traction element 4 Compensatingelement 5 Holder 6 Spring 7 Spring 8 Sleeve 9 Support disc 10 Lockingdisc 11 Bushing 12 Abutment 13 Abutment 14 Projection 15 Spring 16Spring

What is claimed is:
 1. An infinitely variable friction gear having atleast two transmission unite, each transmission unit comprising an inputdisc provided coaxially with the input shaft and having a toroidallyshaped inside surface, and an output disc arranged coaxially with theinput shaft and having a toroidally shaped inside surface, such that ineach case an input disc and an output disc form a pair, several frictionwheels, which are arranged and are able to swivel between the pairs ofinput discs and output discs, and each of which is mounted on a carrier,for the transfer of a torque from the input disc to its associatedoutput disc by swivelling of the carriers and so too of the frictionwheels and a traction element which winds around the ends of thecarriers essentially in a circle and which, to produce a synchronousswivelling movement in opposite directions, is arranged in the form or afigure-8 with its crossover point mid-way between the two carriers,wherein with each carrier of a transmission unit there is associated acompensating unit (4) which effectively couples the two carriers (1, 2)of the transmission unit in such manner that when a differential angleoccurs between the two carriers, a restoring force is exerted upon thecarriers.
 2. The infinitely variable friction gear according to claim 1,wherein the first and second compensating elements (4) are connectioncomponents inserted in the contiguous loop of the traction element (3).3. The infinitely variable friction gear according to claim 1, whereineach compensating element (4) comprises a support disc (9) whichcontacts a spring (6) surrounded by a sleeve (8) and fitted in a bushing(11) so that the support disc (9) can be displaced relative to thebushing (11) against the force of another spring (7), and one section ofthe traction element (3) is centrally attached to the displaceablesupport disc (9) while the other end of the traction element (3) isattached to an end portion of the bushing (11).
 4. The infinitelyvariable friction gear according to claim 1, wherein the first andsecond compensating elements (4) are provided as a component of each ofthe respective first and second carriers (1, 2).
 5. The infinitelyvariable friction gear according to claim 1, wherein each compensatingelement (4) comprises two springs (15, 16), one end of each spring isattached to a holder (5) for the traction element (3) and the other endof each spring is attached to a projection (14) of the respectivecarrier (1), and the projection (14) swivels between two abutments (13,12) delimiting a recess in the holder (5).
 6. The infinitely variablefriction gear according to claim 5, wherein a first transmission unithaving a first input disc supported coaxially with an input shaft and afirst output disc also supported coaxially with the input shaft, thefirst input and first output shaft being variably rotationally connectedby a first friction wheel mounted on a first carrier for the transfer ofa torque between the first input disc and the associated first outputdisc; a second transmission unit having a second input disc supportedcoaxially with the input shaft and a second output disc also supportedcoaxially with the input shaft, the second input and second output shaftbeing variably rotationally connected by a second friction wheel mountedon a second carrier for the transfer of a torque between the secondinput disc and the associated second output disc; a connective elementconnecting the first carrier in the first transmission unit with thesecond carrier in the second transmission unit to produce a mutualsynchronous swiveling movement between the first and second camera inopposite directions; and wherein the traction element is a contiguousloop arranged in the form of a figure eight defining a crossover pointmid-way and having at least a compensating in between the two carrierseffectively couple the first and second carriers (1, 2) of therespective transmission units and at least first compensating unit (4)is coupled with the traction element in such a manner that when adifferential angle occurs between the first and second swivelingcarriers, a spring restoring force is exerted upon the carriers.
 7. Theinfinitely variable friction gear according to claim 6 wherein thecompensating elements are integral with the contiguous loop of thetraction element.
 8. The infinitely variable friction gear according toclaim 6 wherein the compensating elements are integral with the firstand second swivelling carriers.